docs: def is_vertical_coordinate(var_name, var):
      """
      Determines if a variable is a vertical coordinate variable
  
      4.3
      A vertical coordinate will be identifiable by: units of pressure; or the presence of the positive attribute with a
      value of up or down (case insensitive).  Optionally, the vertical type may be indicated additionally by providing
      the standard_name attribute with an appropriate value, and/or the axis attribute with the value Z.
      """
      # Known name
      satisfied = var_name.lower() in _possiblez
      satisfied |= getattr(var, 'standard_name', '') in _possiblez
      # Is the axis set to Z?
      satisfied |= getattr(var, 'axis', '').lower() == 'z'
      is_pressure = units_convertible(getattr(var, 'units', '1'), 'dbar')
      # Pressure defined or positive defined
      satisfied |= is_pressure
      if not is_pressure:
          satisfied |= getattr(var, 'positive', '').lower() in ('up', 'down')
      return satisfied